Question : A certain sum of money amounts to 3 times itself in 13 years when interest is compounded annually at a certain interest rate per annum. In how many years will the initial sum amount to 9 times itself at the same interest rate per annum, also compounded annually?
Option 1: 32 years
Option 2: 26 years
Option 3: 30 years
Option 4: 20 years
Correct Answer: 26 years
Solution :
Given: A certain sum of money amounts to 3 times itself in 13 years when interest is compounded annually at a certain interest rate per annum.
Use the formula,
Let the sum be INR
According to the question,
⇒
On squaring both sides of the equation (1),
⇒
⇒
⇒
So, the required number of years is 26.
Hence, the correct answer is 26 years.
